404 DR. G. 8. BRADY ON THE OSTRACODA 
behind, height equal to nearly half the length ; anterior extremity rounded, subtruncate ; 
posterior produced in the middle into a very acute beak, the upper half being obliquely 
truncate and jagged, the lower half excavated into two large rectangular indentations ; 
dorsal margin straight, ventral slightly sinuated. Outline as seen from above lancet- 
shaped, with a large triangular projection in the middle, behind; widest behind the 
middle, width equal to nearly two thirds of the length; the anterior extremity is 
pointed and broadly rounded, as a lancet; lateral margins nearly straight to near the 
hinder extremity, then suddenly sinking so as to form one and then a second rectan- 
gular excavation; posterior extremity acuminate. End view irregularly arcuate, width 
considerably greater than the height; surface of the shell irregularly waved and 
nodulated, the posterior portion marked by two prominent and sharply defined trans- 
verse ridges, which end below in sharp rectangular processes, and above are continued 
in longitudinal curves toward the middle of the valves. Length 75 inch (0°60 millim.). 
A few specimens only found, in the Pectunculus-bed (Sables inférieurs) and zone a 
Bryozoaires (Sables moyens). It has been found by M. Bosquet in several Eocene 
deposits in France and Belgium, by Egger in the Miocene of Orenburg, and by Speyer 
in the Eocene of Cassel. 
CYTHEROPTERON PIPISTRELLA, noy. sp. (Plate LXIX. figs. 2 a—2 d.) 
Carapace, as seen from the side, subrhomboidal, with a very large and acutely produced 
triangular aleform process, which projects below the middle of the ventral margin ; 
anterior extremity rounded, posterior produced in the middle into a wide truncated 
beak; dorsal margin excessively arched, gibbous, highest in the middle; ventral 
margin convex, hidden in the middle by the projection of the ventral ala. Seen from 
above, broadly sagittate, the lateral ale spreading widely, and forming behind the 
middle of the shell two acute backward-pointing processes, between which and the 
posterior extremity the margins form a deeply excavated arch; the extreme width 
between the apices of the alz is just equal to the length of the shell. End view acutely 
triangular, the lateral margins nearly straight, ventral margin deeply arched and 
obscured in the middle by a triangular projection formed by the anterior margin. 
Surface smooth; lateral ale channelled and marked by a deep hollow at the base. 
Length 35 inch (1 millim.). 
This very fine species occurred not uncommonly in the Sables moyens (zone a Bryo- 
zoaires. 
Genus ByrHocyTHERE, G. O. Sars. 
Valves subequal, smooth or very sparingly sculptured, almost destitute of hairs; thin 
and fragile; hinge-joint quite simple, or composed of a slight bar and furrow; no 
teeth. Upper antennz elongated, 7-jointed; second joint large and thick, with a seta 
on each margin, the other joints much narrower. Lower antenn moderately robust, 
4-jointed ; second joint large. Mandibles strongly toothed ; palp 4-jointed, with a well- 
